function calculateRentalCashFlow() {
// Get Input Values
var price = parseFloat(document.getElementById('rpPrice').value) || 0;
var downPercent = parseFloat(document.getElementById('rpDownPayment').value) || 0;
var interestRate = parseFloat(document.getElementById('rpInterestRate').value) || 0;
var years = parseFloat(document.getElementById('rpLoanTerm').value) || 0;
var closingCosts = parseFloat(document.getElementById('rpClosingCosts').value) || 0;
var rent = parseFloat(document.getElementById('rpRent').value) || 0;
var taxYear = parseFloat(document.getElementById('rpPropertyTax').value) || 0;
var insuranceYear = parseFloat(document.getElementById('rpInsurance').value) || 0;
var hoaMonth = parseFloat(document.getElementById('rpHOA').value) || 0;
var vacancyPercent = parseFloat(document.getElementById('rpVacancy').value) || 0;
var repairsPercent = parseFloat(document.getElementById('rpRepairs').value) || 0;
var capexPercent = parseFloat(document.getElementById('rpCapex').value) || 0;
var managementPercent = parseFloat(document.getElementById('rpManagement').value) || 0;
// Mortgage Calculation
var downAmount = price * (downPercent / 100);
var loanAmount = price – downAmount;
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = years * 12;
var monthlyMortgage = 0;
if (interestRate > 0) {
monthlyMortgage = loanAmount * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
} else {
monthlyMortgage = loanAmount / numberOfPayments;
}
// Operating Expenses
var vacancyCost = rent * (vacancyPercent / 100);
var repairsCost = rent * (repairsPercent / 100);
var capexCost = rent * (capexPercent / 100);
var managementCost = rent * (managementPercent / 100);
var monthlyTax = taxYear / 12;
var monthlyInsurance = insuranceYear / 12;
var totalOperatingExpenses = monthlyTax + monthlyInsurance + hoaMonth + vacancyCost + repairsCost + capexCost + managementCost;
var totalExpenses = totalOperatingExpenses + monthlyMortgage;
// Cash Flow
var monthlyCashFlow = rent – totalExpenses;
var annualCashFlow = monthlyCashFlow * 12;
// Metrics
var totalCashInvested = downAmount + closingCosts;
var cashOnCash = 0;
if (totalCashInvested > 0) {
cashOnCash = (annualCashFlow / totalCashInvested) * 100;
}
var monthlyNOI = rent – totalOperatingExpenses;
var annualNOI = monthlyNOI * 12;
var capRate = 0;
if (price > 0) {
capRate = (annualNOI / price) * 100;
}
// Display Results
document.getElementById('resMortgage').innerText = "$" + monthlyMortgage.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resExpenses').innerText = "$" + totalExpenses.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resNOI').innerText = "$" + monthlyNOI.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
var cashFlowEl = document.getElementById('resCashFlow');
cashFlowEl.innerText = "$" + monthlyCashFlow.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2});
cashFlowEl.style.color = monthlyCashFlow >= 0 ? '#27ae60' : '#c0392b';
var cocEl = document.getElementById('resCoC');
cocEl.innerText = cashOnCash.toFixed(2) + "%";
cocEl.style.color = cashOnCash >= 0 ? '#27ae60' : '#c0392b';
document.getElementById('resCapRate').innerText = capRate.toFixed(2) + "%";
document.getElementById('rpResult').style.display = 'block';
}
Mastering Your Rental Property Cash Flow
Investing in real estate is one of the most reliable ways to build long-term wealth, but not every property is a good investment. The difference between a profitable asset and a money pit often comes down to one critical metric: Cash Flow.
This Rental Property Cash Flow Calculator is designed to give investors a comprehensive view of the financial performance of a potential rental unit. Unlike simple mortgage calculators, this tool accounts for the "hidden" costs of ownership—vacancy, maintenance, capital expenditures (CapEx), and property management—which are often overlooked by beginners.
How to Interpret the Results
Understanding the output of the calculator is essential for making informed investment decisions:
Monthly Cash Flow: This is your "take-home" money after all expenses and mortgage payments are made. Positive cash flow means the property pays for itself and generates profit. Negative cash flow means you are paying out of pocket to hold the property.
Cash on Cash Return (CoC): This metric measures the annual return on the actual cash you invested (down payment + closing costs). It allows you to compare real estate returns against other investments like stocks or bonds. A CoC of 8-12% is generally considered a strong return in many markets.
Cap Rate (Capitalization Rate): This calculates the rate of return on the property based on the Net Operating Income (NOI) assuming you paid all cash. It helps you compare the profitability of the property itself, independent of financing terms.
Net Operating Income (NOI): The total income minus operating expenses, excluding the mortgage. This number is crucial for commercial lending and determining the intrinsic value of the asset.
Why Expenses Estimates Matter
Many new investors fail because they underestimate expenses. This calculator encourages you to input estimates for:
Vacancy: Properties won't be rented 365 days a year. A 5-8% vacancy rate helps account for turnover periods.
CapEx: Roofs, HVAC systems, and water heaters eventually break. Setting aside 5-10% of monthly rent ensures you have funds ready when big repairs are needed.
Property Management: Even if you plan to self-manage, you should account for your time or the future possibility of hiring a manager (typically 8-10% of rent).
Use this tool to analyze multiple scenarios. What happens if the interest rate rises by 1%? What if you raise the rent by $100? By stress-testing your numbers, you can invest with confidence and minimize risk.